Thermoregulation of free-ranging diamond pythons, Morelia spilota (Serpentes, Boidae)

Temperature-sensitive radiotransmitters were implanted in 18 free-ranging diamond pythons (Morelia spilota), and the snakes monitored for 4-34 mo. Body temperatures rose during a period of morning basking to between 28 and 30 C then fell gradually until the following morning. Unlike many other heliothermic reptiles, diamond pythons generally showed only one period of basking each day. Overt shuttling behavior did not occur, but behavioral modifications such as postural adjustments and the use of insulated microhabitats were used to reduce the rate of heat loss. Body temperatures were lower on cloudy days than on clear days, mainly because of reduced opportunities for basking. Mean body temperatures on clear days were lower in winter than in other seasons, mainly because of higher cooling rates. On clear days, snakes under cover were relatively cool (mean ± SD = 23.6 ± 5.35 C), and much warmer when they were active (27.7 ± 4.26 C). On cloudy days, body temperatures were lowest when snakes were coiled in the open (20.9 ± 3.00 C) and highest when snakes were basking (25.4 ± 3.93 C) and moving (25.4 ± 4.08 C). Thermoregulation of large terrestrial snakes may be profoundly influenced by their high but variable thermal inertia: low heating rates militate against shuttling heliothermy, but behavioral and physiological control of cooling rates confers an ability to remain relatively warm even when ambient temperatures fall rapidly. In nocturnal ambush predators like the diamond python, heat-conserving behaviors (coiling immobile in sheltered microhabitats) are compatible with foraging and may extend the range of times and ambient temperatures over which the snake can capture prey.